isl_test.c: generalize isl_map_lexmin tests
isl_test.c: generalize isl_map_lexmin tests

This will make it easier to add additional isl_map_lexmin tests.

Signed-off-by: Sven Verdoolaege <e5350bbed4977f5eb8ae1dc6abd9ae59d21ace75@kotnet.org>

UBERTC/isl,tobig/isl,PollyLabs/isl,UBERTC/isl,PollyLabs/isl,inducer/isl-mirror,inducer/isl-mirror,Meinersbur/isl,inducer/isl-mirror,UBERTC/isl,tobig/isl,tobig/isl,nicolasvasilache/isl,PollyLabs/isl,PollyLabs/isl,Meinersbur/isl,Meinersbur/isl,inducer/isl-mirror,tobig/isl,nicolasvasilache/isl,nicolasvasilache/isl,inducer/isl-mirror,UBERTC/isl,nicolasvasilache/isl,Meinersbur/isl,PollyLabs/isl,nicolasvasilache/isl